Knowing whether a patient has clinical nephrotic syndrome and knowing the degree of podocyte foot process effacement can be helpful diagnostic clues in separating “primary” from “secondary” forms of focal segmental glomerulosclerosis (FSGS). For example, in a patient with the nephrotic syndrome whose biopsy shows FSGS lesions and no significant immune deposits by immunofluorescence, the presence of global effacement of podocyte foot processes by electron microscopy (as seen in Fig 1) provides support for a “primary” FSGS (see reference).